I. Field of the Invention
This invention pertains to the art of optical fiber cable tubing bundles and more particularly to cable tubing bundles intended for vertical installation.
II. Description of the Related Art
Presently, cable tubing bundles intended for installation in the vertical shafts of buildings must meet the standard for safety imposed by Underwriters Laboratories, Inc. for flame propagation height of electrical and optical-fiber cables installed vertically in shafts. UL 1666 describes the Underwriters Laboratories, Inc.'s standard test method for determining values of flame propagation height for electrical and optical-fiber cables installed vertically in shafts. To be acceptable, the flame propagation height for a vertically installed cable cannot equal or exceed 12 feet, 0 inches. The purpose of the test is to insure that vertically installed cables comply with ANSI/NFPA 70-1987: section 725-38(b)(2), exception to section 760-28(c)(2), section 770-6(b), section 800-3(b)(2), and section 820-15(b) of the National Electric Code.
The test apparatus consists of a test chamber; burner apparatus; and, temperature and flow measurement instrumentation. Two samples of cable construction of multiple seventeen and one half (171/2) feet lengths are tested. A test flame is applied to one end of the cable construction for thirty (30) minutes. After thirty (30) minutes, the test flame is extinguished and the maximum height of continuous cable damage is measured and recorded. Damage is recorded as having occurred when the combustible material comprising the cable is softened ("melt"), partially consumed ("char"), or completely consumed ("ash").
Optical fiber cable tubing bundles designed to meet or exceed the UL 1666 standard set for determining flame propagation height of cables mounted vertically in shafts, have relied on the thermoplastic material used to off gas when heated or burned creating a smothering effect, stopping flame propagation.